British Prime Minister David Cameron said his renegotiation of Britain's ties with the European Union was "bloody hard work" but that he would not be rushed into naming a date for a referendum on membership, London's Sunday Telegraph reported.

On the eve of an annual gathering of his ruling Conservative Party, Cameron urged his lawmakers and supporters to show patience over the issue of Europe, which is likely to dominate the conference in the northern English city of Manchester.

For at least a generation, Cameron's party has been riven by a conflict over Europe that contributed to the downfall of both Margaret Thatcher and John Major, the last two Conservative prime ministers.

Under pressure from lawmakers who feared the electoral success of the anti-EU UK Independence Party, Cameron in 2013 promised a referendum on membership by the end of 2017, though many analysts and campaigners expect it to be called next year.

In what the newspaper said was a signal that the referendum will not be held early next year, Cameron said his EU counterparts will have "plenty of time" to consider his requests for a new relationship with Brussels.

He is demanding that EU leaders allow Britain to cut employment benefits for EU migrants and allow London to prevent eurozone rules that London considers would hurt British interests.

But as many as one in five of Cameron's lawmakers is likely to vote to leave the EU, research from the Open Europe think tank showed Friday, indicating the scale of the divide over Europe in the ruling Conservative Party.

Cameron favors staying in a reformed EU but has said he will rule nothing out if he cannot secure what he wants. A new biography of Cameron written by Michael Ashcroft says that Cameron has repeatedly said privately that he does not want to leave the EU.

The book also said that German leader Angela Merkel believes Cameron has made a series of serious errors in his push for a new EU deal for Britain.